Circuit modification: powering a VU meter board

[blackeyeliner]

So I've built my Crack with a lot of DIYing on the casing - I made an additional housing for VU meters, installed VU meter board inside the case etc. However, the meter board is powered with external 12V power supply, which is obviously not an elegant solution... Is there any way to get 12V from Crack power supply and not influencing the sound?

 

[Paul Birkeland]

How much 12V current do you need?

 

[blackeyeliner]

How much 12V current do you need?

Very little: 0.1A max, typically 0.08.

 

[Paul Birkeland]

If it's that little, you could try adding a voltage doubler to get +12V.

 

[Paul Joppa]

Does the 12v need to be grounded? Does the audio input to the meter board need to have the same ground as the 12v power supply? If so, be sure to remove the heater winding ground before grounding a doubler supply. It may or may not affect the hum level - just be sure to check this.

 

[blackeyeliner]

If it's that little, you could try adding a voltage doubler to get +12V.

Yes, it's definitely very little. Unfortunately, I'm not very experienced in electronics, could you elaborate a little more on how voltage doubler could be implemented in a Crack?

 

[blackeyeliner]

Does the 12v need to be grounded? Does the audio input to the meter board need to have the same ground as the 12v power supply? If so, be sure to remove the heater winding ground before grounding a doubler supply. It may or may not affect the hum level - just be sure to check this.

12V needs to be grounded.

Audio input uses a different ground other than 12V power supply, they are isolated in the board - as I understand, for the sake of hum. Right now the board is powered with a separate power supply and it does not affect hum in any way.

However, I don't really understand how to make a doubler and how to apply it to the existing circuit yet But I am sure that with little help I will be able to do it.

 

[Paul Birkeland]

could you elaborate a little more on how voltage doubler could be implemented in a Crack?

I would do some reading online about voltage doublers, then come back with specific questions.

-PB

 

[blackeyeliner]

I would do some reading online about voltage doublers, then come back with specific questions.

-PB

I understand the theory how voltage doubler works - I understand (or at least I suppose I do) that if I know reliably a 12V point in my circuit, I can add voltage doubler to this point and get 12V not altering the voltage of the circuit itself.

However, it's really unclear to me to which point to hook it up to and what scheme of a voltage doubler to use (my research showed that there are dozens).

 

[Paul Birkeland]

I understand the theory how voltage doubler works - I understand (or at least I suppose I do) that if I know reliably a 12V point in my circuit, I can add voltage doubler to this point and get 12V not altering the voltage of the circuit itself.

A voltage doubler gives you 12V DC out of about 6V AC, but with a ton of ripple.  This can be added to the 6.3V winding in the Crack, provided you don't need much current.  The ground reference of the winding may have to be removed, but this depends on whether you need a specific 12V ground reference.

-PB

 

[blackeyeliner]

A voltage doubler gives you 12V DC out of about 6V AC, but with a ton of ripple.  This can be added to the 6.3V winding in the Crack, provided you don't need much current.  The ground reference of the winding may have to be removed, but this depends on whether you need a specific 12V ground reference.

-PB

It gets clearer. So I hook up a scheme like this:

to a 6V AC winding of the crack and I get 12V DC which will be pretty ripply, but should I guess work for my purpose of powering the driver board.

In case I don't need a specific ground reference for the audio signal in the power wiring I just use the + and - wires of the 6V AC winding? The board has separate input for audio (left, right and ground reference) and for power (+12V and ground).

If that is right, I need to understand now is where this 6V AC winding in the Crack is and what capacitance I need for capacitors. Everything else seems to be pretty simple.

I am really sorry for my lack of knowledge in electronics, but I am really trying. Big thanks for helping me out with this.

 

[Grainger49]

The 6V AC winding is the heater wires.  They appear on A4/5 and A9.

 

[Paul Birkeland]

In case I don't need a specific ground reference for the audio signal in the power wiring I just use the + and - wires of the 6V AC winding? The board has separate input for audio (left, right and ground reference) and for power (+12V and ground).

Set your meter for continuity, then measure between the ground pad on the +12V pair and a ground pad on the ground reference by the L/R pads.  Are they connected?

 

[blackeyeliner]

Set your meter for continuity, then measure between the ground pad on the +12V pair and a ground pad on the ground reference by the L/R pads.  Are they connected?

Just done it. No, they are not - they show around 800-900K Ohms between them.

 

[Paul Birkeland]

That's a decent sign that you can add the doubler to the Crack and not move the grounding.  I would recommend wiring up the doubler to give +/-6V, which would mean that the grounded terminal on the 6.3V winding should go to the junction of the two caps.

Cap sizes are determined by how much ripple you can tolerate, I'd say start with 4700uf and see how that works.

-PB

 

[blackeyeliner]

That's a decent sign that you can add the doubler to the Crack and not move the grounding.  I would recommend wiring up the doubler to give +/-6V, which would mean that the grounded terminal on the 6.3V winding should go to the junction of the two caps.

Cap sizes are determined by how much ripple you can tolerate, I'd say start with 4700uf and see how that works.

-PB

So it's exactly like it's done on the scheme I proposed (this one - http://www.daenotes.com/images/full-wave-voltage-doubler.png), right? I am ready to go in this case and will do it by weekend.

 

[Paul Birkeland]

Yeah, I would put some resistors across each of those caps, 1K ought to be enough, wattage rating isn't particularly important with only 6V across them, 1/8W is enough.

 

[blackeyeliner]

Yeah, I would put some resistors across each of those caps, 1K ought to be enough, wattage rating isn't particularly important with only 6V across them, 1/8W is enough.

Across - you mean, in parallel? Will do. Just out of curiosity, why is that desirable to do?

 

[Paul Birkeland]

It's generally good practice.  IMO, it matters more for high voltage circuits, where you really want to know that each cap is seeing an equal amount of voltage.

 

[blackeyeliner]

I made it and - it worked! However, I messed up with polarity while plugging it in and one of the capacitors is destroyed, so I will have to replace it. However, the doubler gave me 13V DC which was pefrectly fine for powering the board.

Interestingly enough, while looking at the board I understood it could be powered with AC, as it has diode bridge on it (and AC IN marking). However, directly hooking up 6.3V AC from Crack to the board did not work - it barely produced enough voltage to light up the backlights, and meters did not work. With doubler however, it works just fine.